Bygdelag are organizations comprised of descendants who emigrated from specific localities in Norway to North Amierica. See Bygdelagenes Fellesraad at: http://www.fellesraad.com/Explore-Bklet.pdf
From the website above find a copy of their most up to date printable brochure. Here you will find contact information to people with information about emigrants from most places in Norway. Find the contact information for the person representing the area your ancestors came from in Norway, as they often have detailed information about most immigrants.